INTEODUCTION. XXV 



want of appropriate and congenial places for their growth and 

 dispersion, which extensive bodies of water aiford ; something 

 being doubtless due, as we have lately seen, to climate and 

 insularity of position. Omitting a few insignificant ponds, 

 pools and dams, of mostly recent and artificial construction, 

 the natural drainage of the island is effected chiefly by some 

 half-dozen or so of sluggish streamlets, fed by the numerous 

 fine springs with which the island abounds, that break out at 

 the base of the chalk ranges, and find their way, through 

 narrow devious channels, to the sea. The water of these 

 streams is mostly turbid, from the detritus of the rocks they 

 flow over ; and their motion, though slow, combined with the 

 depth and narrowness of the channels they pass along, are all 

 unfavourable to the growth of such purely aquatic plants as 

 require the clear, broad, shallow and tranquil element for their 

 habitation. Moreover, the water of those streams that mean- 

 der through the boggy valleys of the Medina and Main River, 

 and of the drains and ditches communicating with them, is 

 contaminated with peroxide of iron from the ferruginous sand- 

 stone, or the decomposition of the pyritic nodules that abound 

 in the chalk and tertiary formations, and which impregnation 

 cannot but be injurious to some aquatic vegetables. From 

 all these causes united it doubtless happens that the following 

 genera and species of true water-plants are strangers on this 

 side of the Solent : — 



Nymphffla (introduced ?) Ceratophyllum ? 



Nuphar Stratiotes (introduced) 



Sagittaria Acorus 



Hottonia Actinocarpus 

 Hydrocharis (introduced) 



Whilst, of species belonging to genera of which representatives 

 occur m the island, we miss — 



Sium latifolium Potaraogeton perfoliatum 



CEnanthe Phellandrium Nasturtium amphibiura 



„ fluviatile Glyceria aquatioa 



Myriophylluin verticillatum 



